Designing Ti-Alloys Using 3D Printing for Load-Bearing Applications: Enhanced Biocompatibility, Minimized Tribo-Corrosion and Inherent Infection Resistance

Metal 3D Printing was utilized to design novel Ti-alloys for load-bearing implant applications focusing on improving biocompatibility, minimizing bio-tribo-corrosion and related metal ion release, and adding inherent infection resistance. Successful alloy design can minimize adverse local tissue response (ALTR) from total hip implants (THAs) taper corrosion and septic loosening due to polymicrobial infections, eventually reducing implant failure in vivo. In one case, we designed a Ti-Ta-Cu alloy where Cu offers intrinsic microbial resistance and Ta-enhanced biocompatibility to mitigate potential Cu toxicity. Instead of using Ti6Al4V alloy, vanadium and aluminum contents were reduced to design a Ti3Al2V alloy for metallic implant applications. The biological and mechanical properties of Ti3Al2V alloy were measured. A 10% Ta and 3% Cu were added to the Ti3Al2V alloy to enhance biocompatibility and impart inherent bacterial resistance. Additively manufactured implants were investigated for resistance against <i>pseudomonas aeruginosa</i> and <i>staphylococcus aureus </i>strains of bacteria up to 48 h. A 3% Cu addition to Ti3Al2V showed an improved antibacterial efficacy, between 76 and 81% higher than CpTi and Ti6Al4V. Mechanical properties for Ti3Al2V-10Ta-3Cu alloy were measured, demonstrating excellent fatigue resistance, good shear strengths, and better tribological characteristics than Ti6Al4V. <i>In</i> <i>vivo</i> studies using a rat distal femur model showed improved early-stage osseointegration for alloys with 10%Ta addition than CpTi and Ti6Al4V. Ti6Al4V-ZTA-HA metal matrix composites were designed and investigated for load-bearing femoral heads in another alloy design. The composites were fabricated via 3D Printing. A rabbit distal femur 16-week <i>in vivo</i> study for implantation and histological characterization was conducted. An induced <i>in vitro</i> 16-week applied potential polarization study of the Ti6Al4V and Ti6Al4V-zirconia toughened alumina (ZTA)-hydroxyapatite (HA)-based composites was conducted to investigate the coupled taper-corrosion behavior. The Ti6Al4V-ZTA-HA composites displayed increased hardness, decreased wear volume, increased surface passivation during tribological testing, and faster re-passivation post-tribological testing, validated by increased contact resistance and more cathodic open circuit potential. Finally, a first-of-a-kind table-top joint simulator was designed and manufactured to simulate volumetric tribo-corrosion of femoral heads. The simulator mimics the gait-like motion of the hip joint. Ti6Al4V+ZTA+HA metal matrix composite femoral heads were produced via 3D Printing. The ability to move into volumetric articulating-based testing has shown promising results for improving these innovative materials to address the shortcomings of currently used metallic biomaterials in load-bearing orthopedic devices where corrosion and wear are of concern. The presentation will discuss 3D Printing-based alloy design and related characterization of next-generation Ti-alloys for load-bearing implants.